Eva and her husband Hans Kristian Rausing, heir to the $10bn Tetra Pak fortune, were both friends of Prince Charles. Eva was a trustee of and major donor to his pet architecture charity, The Prince's Foundation for Building Community, and was also a co-patron of Action on Addiction with Kate Middleton.

Hans K, as he is known in London, 49, is still being treated in hospital today after being arrested on Tuesday when detectives discovered the body of Eva, 48 in a bedroom during a search of the couple’s home. He had been stopped for driving erratically earlier in the day and found to have drugs on him.

It has now emerged that as part of the investigation into what detectives are describing as Eva's “unexplained” death, they are examining how long she might have lain dead in her home before police arrived.

A postmortem on Tuesday proved inconclusive and further tests are being carried out to establish the cause of death, which could have taken place up to a week ago.

Police from the London Metropolitan police’s homicide and serious crime command have yet to interview Mr Rausing. Scotland Yard said he remained under arrest but had been transferred to hospital for treatment and police officers were present. His condition is not thought to be life-threatening and crime correspondent Sandra Laville of the Guardian is reporting that he is being treated in the Maudsley hospital for drug-related issues.

The Rausing family is worth some $10billion thanks to their invention of the Tetra Pak cartons.

Although it was hard not to notice the increasingly haggard appearance of the Rausings when they were out and about, few suspected the true reason for their decline. Their secret only came out in April 2008, when Eva Rausing attended the American Embassy to renew her US passport.

All bags are searched on entry. Mrs Rausing cheerfully submitted to the process – evidently forgetting that she had left 2.5 grams of heroin and 10 grams of crack cocaine in her purse. The police were called, and a further search of the couples palatial London home turned up 5.63g of crack cocaine, 2.9g of heroin and almost 52g of high-purity cocaine.

Although the amount of drugs the Rausings had been found with would have earned a street pusher a considerable spell in jail, in August 2008, all charges were suddenly dropped at Westminster Magistrates Court after what was described as a “protracted correspondence” between their lawyers and the Crown Prosecution Service. This was despite the fact that in June, while on bail, a car registered to Hans Rausing was spotted fleeing the scene of an accident.

Despite massive public outrage about the handling of the Rausing’s case, and suspicions that their donations to charities of millions of dollars a year were the true reason they enjoyed such leniency, Prince Charles, who in 2004 had personally appointed Mrs Rausing as a trustee of his charity, the Prince’s Foundation for the Built Environment, took the extraordinary decision to publicly back Eva Rausing.

An aide to the Prince told the Daily Mail at the time: “The Prince’s charities work with young people, many of whom have had problems with drugs. They aim to give these people a second chance to help them rebuild their lives. It would therefore be hypocritical for the Prince not to give Eva Rausing a second chance.”

Chief executive of the Prince’s Foundation Hank Dittmar, a former adviser to President Clinton, said at the time: “We support Eva Rausing in her efforts to overcome her problems and look forward to her completion of her treatment programme. She remains a dedicated member of the Foundation board of trustees contributing to the charity’s education work.”

Questions are now being asked as to whether the failure of the authorities to administer a short sharp shock to the Rausings in the form of a jail term in 2008, and their continued acceptance at the highest levels of society including royalty, contributed to the continuation of their habit and Eva’s tragic death.